"He reconsidered when he realized concrete doesn't burn."

He wasn't a chemist.

Chlorine Triflouride

Chlorine trifluoride, ClF₃, or “CTF” as the engineers insist on calling it, is a colorless gas, a greenish liquid, or a white solid. … It is also quite probably the most vigorous fluorinating agent in existence—much more vigorous than fluorine itself. … It is, of course, extremely toxic, but that's the least of the problem. It is hypergolic with every known fuel, and so rapidly hypergolic that no ignition delay has ever been measured. It is also hypergolic with such things as cloth, wood, and test engineers, not to mention asbestos, sand, and water—with which it reacts explosively. It can be kept in some of the ordinary structural metals—steel, copper, aluminum, etc.—because the formation of a thin film of insoluble metal fluoride which protects the bulk of the metal, just as the invisible coat of oxide on aluminum keeps it from burning up in the atmosphere. If, however, this coat is melted or scrubbed off, the operator is confronted with the problem of coping with a metal-fluorine fire. For dealing with this situation, I have always recommended a good pair of running shoes.

Scorches concrete and makes it mildly explode. Turns your bones to chalk if it touches your skin. Only real treatment is soaking your now extremely painful extremity in a calcium bath and hoping your heart wont stop while you wait for someone to get to you with an injection that might help a little.

Woodchipper

You can put them on the workbench for some plastic.

Or, yeah, woodchipper.